The invention relates to a cabinet for housing electronic plug-in cards that have a front, a back, a front card basket for inserting plug-in cards from the front and a rear card basket for inserting plug-in cards from the back. The cabinet further comprises a first vertical backplane with a front side and a rear side, wherein the first backplane is attached to the end of the front card basket such that its front side points to the front of the cabinet, and a second backplane with a front side and a rear side, wherein the second backplane is arranged in parallel and at a distance on the rear side of the first backplane such that the front side of the second backplane points to the back of the cabinet. Distance pieces connect the two backplanes with each other.
Such a cabinet is used for modular computer systems in the telecommunications industry. According to new or future standards for such modular computer systems such as Advanced TCA Extension, the rear card basket has the same size as the front card basket. As a result plug-in cards of the same size can be housed both in the front and in the rear card basket.
When installing the electronic components the first vertical backplane is initially screwed to the housing. Thereafter the second backplane is attached to the rear side of the first backplane by means of distance pieces. Then the plug-in cards are pushed onto the first or the second backplane in the front and the rear card basket.
When manufacturing the backplanes their thickness is subject to a manufacturing tolerance of approx. ±10%. Since the length of the distance pieces is also subject to a certain manufacturing tolerance, the distance between the front sides of the two backplanes mounted on top of each other comprises a correspondingly large overall tolerance. This tolerance is not acceptable for the majority of applications.
Due to the overall tolerance the mounting position of the second backplane in the cabinet varies considerably. When for example plug-in modules are pushed onto the second backplane, the varying overall tolerance in the worst case can have the effect of some plug-in cards protruding from the rear card basket. The front plates of the plug-in modules do then not finish flush with the rear card basket. As a result the cabinet may not be correctly closed on its back.
The document “Progress in Advanced TCA for Instrumentation, ATCA Summit 2012”, on page 11 describes an arrangement of two backplanes, wherein the second backplane is attached on top of the first backplane with the aid of distance pieces. Both the first and the second backplane have plug-in cards of the same size inserted into them. Page 11 also shows cabinets into which such an arrangement is installed.
The document “ATCA Summit 2011, Advanced TCA Extensions PICMG 3.7 Mechanical”, 2 Nov. 2012, Eike Waltz, on page 10 discloses a cabinet with two backplanes. The cabinet comprises a front and a rear card basket, wherein both card baskets are of the same size.
U.S. Pat. No. 7,239,528 B1 discloses a cabinet with a front card basket, a rear card basket and a midplane. The midplane is attached to the front card basket, which by means of connecting pieces is connected with the rear card basket. The connecting pieces comprise elongated slots by means of which the rear card basket can be moved relative to the front card basket. Variations in the thickness of the midplane can thus be compensated for by adjusting the rear card basket. This ensures that independently of the thickness tolerance of the midplane, plug-in cards mounted in the rear card basket cannot not protrude from the rear card basket.